It could be the tube but it could be something else too.
The filament should glow visibly in any working glass envelope tube. However, it is relatively rare for a tube to lose its filament (and quit glowing). Sometimes a tube will have dirty contacts where it plugs in. Then wiggling it or unplugging it and plugging it back in will fix it.
Also, on the Rebel 30 you have two sets of output tubes, so loosing one tube shouldn't make both the 6V6 and the EL84 side quit completely.
So, my guess is that there is another issue.
I am assuming that by glowing you mean a dull red (or orange) in the center of the tube. If the whole inner structure of the tube is a somewhat bright red then the inside of the tube is trying to melt. That can also be caused by a bad tube but will mean that tubes and probably other parts will need to be changed.
As jstcrsn stated, you need to be somewhat cautious when working on tube amplifiers. The internal voltages on the output tubes in this amp are likely to be around 400 volts dc. The tubes themselves (in amplifiers we are likely to see) don't actually store voltages (the internal capacitance is too low) but the filter caps in the amplifier can keep an uncomfortably amount of voltage for a few hours (usually it will drop below the potentially fatal range in a half hour or so).
So, if you don't know the safety rules for working around high voltage, find someone who does to do the work.
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